Do you know what he did in his free time? If so, try to fine a job that relates to that. If not, maybe thte next time he and his friends hang ask them about him. Or you could even talk with him your self.

It is harder to motivate older kids. Especially teenagers, because their already wanting to be independent. You should research ways to motivate, read phyciatrisyt journals, go to a professional on this stuff. And if you have to, scare him straight. Show him somehow that his life will be better, and happier with a proper education, and positive motivation. There is no straight answer to this. It's going to take alot of chipping at. But I'd say, the best, most effective thing you can do right now. Don't give up on him yet. He is still young, and in his darkest of times will depend on you. I wish you luck. :).

This is a giant challenge facing many parents.  It is such a large challenge that our society will face a crisis of what I call "Lost Boys" related to all the young men who do not go onto higher education yet refuse to consider wise suggestions such as yours to consider a trade.
But, of course, you are interested in how you can help your son.  You have to first understand him his deep core motivations.  I know you understand him like a father.  But, you have to understand him also as a coach.  What is causing his paralysis?  What are his motivational triggers?  I wrote a book, "Motivate Your Son" that I believe could help you - and I apologize for pitching it here as the solution - but it directly addresses your question in a comprehensive way.  You can find it on Amazon or you can check our website below.